Pumping system for metal-tank rectifiers



\LK. ZWORYKIN ET AL PUMPING SYSTEM FOR METAL TANK RECTIFIERS Filed Aug.3, 1927 17 J6 /2 i; Q E 11:35 IE 1 14 Z5 5 rz m INVENTORS Vla az'mz'r/fZworykin and Errol B, 5/2 and ATTORNEY I nism 8 comprises a cam segment9 bearing Patented June 4, 1929.

UNITED STATES VLADIMIR K. ZWORYKIN,

PENNSYLVANIA, ASSIGNORS, TO

ATE-N T oFF1cE.

CORPORATION, A CORPORATION OF PENNSYLVANIA.

PUMPING SYSTEM FOR METAL-TANK RECTIFIERS.

Application filed August 3, 1927. Serial No. 210,275.

Our invention relates to vacuum pumping systems, and it has particularrelation to such systems utilizing two pumps in series, with aninterstage reservoir in between, into which the high-vacuum pumpexhausts, with automatic means for starting and stopping the fore-vacuumpump in response to the degree of vacuum in the interstage reservoir.

The object of our invention is to provide an improved mechanism andsystem for carrying into effect the object just stated.

Our invention will best be understood by reference to the accompanyingdrawing, the single figure of which is a diagrammatic view of circuitsand apparatus embodying our invention, in a preferred'form, some of theparts being shown in" section, others in elevation and still others bymeans of diagrammatic representation.

Our invention is particularly adapted for evacuating, or maintaining ahigh degree of evacuation in, a metal-tank rectifier, which is indicatedon the drawing at 1, the rectifier being shown, however, ona somewhatreduced scale, in proportion to the other apparatus, for convenience inillustration. Connected to the rectifier tankis a highvacuum pump 2,which may be a mercuryvapor pump of well-known design, connected to thetank through the intermediation of a vacuum'valve 3 which may beautomatically controlled by any suitable mechanism 4, such as that whichis shown and described in the application of E. B. Shand,

' Ser. No. 210,289, filed Aug. 3, 1927.

T he high-vacuumpump 2 discharges into an interstage reservoir 5 whichis, in turn, exhausted by means of a fore-vacuum pump 6, illustrated asbeing of the rotary type, driven by an electric motor 6. In theconnections between the interstage reservoir and the fore-vacuum pump,is provided another.vacuum valve 7 to be operated by a motor mechanism 8which may be as that already referred to.

In particular, the valve-operating mechathe sameon the top of the valvestem 10 and biased toward a valve-closing position by means of a spring11. The cam segment 9 is moved to its valve-opening position by means ofan electric motor 12 which is geared to a worm shaft 13 carrying a worm14 which meshes with a worm gear segment 15 mounted on the same shaft asthe cam segment 9. The worm shaft 13 is movable to a position in whichthe worm is either in or out of engagement with the worm-gearsegment 15by means of a solenoid 16. Any suitable stopping mechanism, such as thatindicated at 17 may be utilized to stop the motor 12 when the-valve hasreached its full-open position.

The operation of the valve-operating .mechanism just mentioned, as wellas the starting and stopping of the pump motor- 6 may be controlled bymeans of a manometer 20 which is connected to the interstage reservoir5' and is thus responsive to the fore-vacuum existing therein. Themanometer may conveniently comprise a glass vessel 21 having a U-shapedtube 22, connected to its bottom portion and terminating in an arm 23extending upwardly alongside the vessel 21. In the upwardly-extendingarm 23, we provide at least one, and preferably two, contact wires 24and 25, and a lower portion of the U-tube is provided with an Iadditional contact member 26. The manometer is partially filled withmercury 27.

In operation, the mercury-vapor pump is capable of pumping from a vacuumof the order of about a micron of mercury, more or less, to afore-vacuum which may vary in pressure up to about 5 or 10 millimetersof mercury, the figures just stated being given for illustrativepurposes only. The rotary pump 6 is capable of pumping from a pressureof a small fraction of a millimeter of mercury, exhausting againstatmospheric pressure.

The accurate measurement of the extremely high vacua utilized in therectifier tank 1 or, in general, in the vessel to be exhausted, isextremely difiieult, particularly when an attempt is made to utilizeautomatic apparatus. On the other hand, the measurement of pressures ofthe order of millimctcrs may be very accurately and simply accomplishedby means of a manometer, such as that which is hereinabove described,and such apparatus readily lends itself to embodiment in automaticequipment.

In operation, the manometer makes a contact between the upper electrode24: and the mercury colunm, when .a predetermlned maximum fore-vacuumpressure of 5 or 6 millimeters is present. The contact of the mercurywith the upper contact electrode 24 is utilized to energize the solenoid28 of a relay 29 for closinga switch 30 which starts the pump motor 6from an auxiliary source of supply, such as the transformer 31. At thesame time, the closing of the switch 30 energizes the valve-openingmotor 12 and the valve-gear magnet 16 for bringing the gears into meshfor the purpose of starting to open the vacuum valve 7 between theinterstage reservoir 5 and the rotary pump 6.

The pump 6 almost immediately attains full speed and very quicklyexhausts the air from the short length of pipe intervening between itand the valve 7, but it takes the valve about eight seconds to fullyopen and about four seconds before it is even partially open.

We have found that there is sufficient time lag in the operation of thevalve to enable the rotary pump to be in effective operation before theopening of the valve. lVe have shown, however, by way of illustration, a

dash-pot 32 associated with the gear-meshing'magnet 16 for delaying themeshing of the worm 14 with the gear segment 15 after the energizationof the gear-shift magnet 16.

Any suitable mechanism may be utilized for stopping the action of therotating pump, either after a predetermined interval, or in response toa predetermined degree of evacuation in the interstage reservoir. Wehave illustrated a combination of both methods of controlling thestopping of the pump.

The operation in response to the predetermined degree of evacuation inthe interstage reservoir is' secured by means of the lower contact wire25, of the manometer, which is connected to the relay magnet 28 throughauxiliary switch contacts 34, which are closed when the relay is closed.Thus, after the relay has been moved to closed position by contact ofthe mercury with the upper electrode 24, the lower electrode 25 maintamsthe energization of the relay until the mercury breaks contact with saidlower electrode. The lower electrode may be placed as close to themercury level in the larger container 21 as mechanical considerationsWlll permit. In ractical operation, the lower contact may e caused toshut off the rotary pump when a vacuum of 1 millimeter,

or even one-half of a millimeter, of mercury is reached in theinterstage reservoir.

After the switch magnet 28 has been deenergizedby the opening of thelower contact member 25 of the manometer, the opening of the relay maybe still further delayed by means of a dash-pot 36 connected thereto insuch manner as to cause the rotary pump to continue to operate for anypredetermined length of time after the deenergization of the relay 29.

operative position, so that it drops downout of engagement with theworm-gear segment 15, thereby permitting the valve-closing spring 11 tosnap the "alve instantaneously to its closed position. It will beunderstood that the dash-pot 32, if used at all. 'will be arranged topermit a substantially unopposed downward movement of the worm shaft 13,but to oppose the upward movement thereof, as indicated in the drawing.

By utilizing an interstage reservoir of sufficient capacity to enablethe mercury pump to discharge into it for a considerable length of timewithout having the forevacuum pressure therein rise to a pressureagainst which the mercury pump cannot operate, and by providing avacuum-responsive device, such as the manometer 20, which responds tomercury columns which are not microscopic in their dimensions, as in thecase of the mercury columns correspondingto the vacuum in the rectifiertank 1, we have been able to provide an extremely simple and reliableautomatic pumping system, as above described.

. We find it highly desirable to operate the mercury pump continuously,in order to preserve as high vacuum as possible in the rectifier tank 1,and also in order to be instantly available, in case of sudden gassingor evolution of gases or sudden. loads on the rectifier. Heretofore, indevices utilizing an automatic response to the vacuum conditions in therectifier to start both of the pumps, there has been a time delay of theorder of three-quarters of an hour before the mercury pump could beheated to an operative temperature, during which time it has beennecessary to keep the valve 3, for example, closed. p

We have found that mercury pumps, as

with the automatic pressure-responsive device thereon, makes suchintermittent operation of the rotary pump feasible.

While we have described our invention in a preferred embodiment andexplained its advantages and operation with respect .to such preferredembodiment, we wish it to be distinctly understood that our descriptionand explanation are largely illustrative, and that changes in degree andin the exact design or arrangement of the parts may be resorted to bythose skilled in the art without sacrificing theessential principles ofour invention. We desire, therefore, that the appended claims shall begiven the broadest interpretation consistent with their wording and theprior art. I

We claim as our invention:

v1. In a vacuum pumping system, the combination with a vessel to bemaintained at a high degree of evacuation, of a high vacuum pump, afore-vacuum pump, an interstage reservoir therebetween, a mechanicallyactuated valve between said interstage reservoir and said fore-vacuumpump, and. means responsive to the fore-vacuum in said interstagereservoir for intermittently starting and stopping said forevacuum pumpand opening and closing said valve, whereby the pressure in saidinterstage reservoir is maintained within predetermined limits.

2. In a vacuum pumping system, the combination with a vessel to bemaintained at a high degree of evacuation, of a high-vacuum pump, afore-vacuum pump, an interstage reservoir therebetween, a valve betweensaid interstage reservoir and said fore-vacuum pump, substantiallyinstantaneously operating closing means for said valve, relatively,slowly operating opening means therefor, means responsive to apredetermined maximum pressure in said interstage reservoir for startingsaid fore-vacuum pump and energizing said valve-opening means, and meansfor simultaneously deenergizing said fore-vacuum pump and rendering saidinstantaneous valve-closing means effective.

3. In a vacuum pumping system, the combination with 'a vessel adapted tobe main tained at a high degree of evacuation, of a J said pump andhigh-vacuum ump adapted to operate continuously, a ore-vacuum pumpadapted to operate intermittently, an interstage reser-. voirtherebetween, a mechanically actuated valve between said interstagereservoir and said fore-vacuumpump, and automatic control means for saidvalve and for said'intermittently operated pump, including meansresponsive to a predetermined maximum pressure in said interstagereservoir for starting said pump and subsequently effecti'ng the openingof said valve, and means operativev at the termination of the desiredintermittent operation of said pump to close the valve and subsequentlydiscontinue the effective operation of the pump.

4. In a vacuum pumping system, the combination with a vessel adapted tobe maintained at a high degree of evacuation, of a high-vacuum pumpadapted tooperate continuously, a fore-vacuum pump adapted to operateintermittently, an interstage reservoir therebetween, a mechanicallyactuated valve between said interstage reservoir and said fore-vacuumpump, and automatic control means for said valve and for saidintermittently operated pump, including a relay adapted, upon actuationto its closed position, to energize mechanism for starting I said pumpand subsequently effecting the opening of said valve, ther adapted, uponmoving to its open position, to cause the closing of the valve and thesubsequent discontinuance of the effective operation of the pump, meansresponsive to a predetermined maximum pressure in said interstagereservoir for effecting the closing of said relay, operative after theclosure of the relay and until the pressure in the interstage reservoirfalls to a predetermined minimum pressure, for holding the relay closed.

5. In a vacuum pumping system, the combination with a vessel adapted tobe main tained at a high degree of evacuation of the order of microns ofmercury, of a highvacuum pump adapted to operate continuously andoperative against a fore-vacuum of the order of millimetersof mercury,an interstage reservoir into which said highvacuum pump discharges, anintermittently operating fore-vacuum pump for maintaining the necessarystage reservoir, a mechanically actuated valve between said interstagereservoir and said fore-vacuum pump, and automatic control means forsaid valve and for said intermittently operated pump, including a relayadapted, upon actuation to its closed position, to energize mechanismfor starting subsequently effecting the opening of said valve, saidrelay ther adapted, upon moving to its open position, to cause theclosing of the valve and said relay being furand further means,-

being fur-" fore-vacuum in said inter- I 1 closed until after themercury level falls below said lower contact. 10

In testimony whereof, we have hereunto subscribed our names this 26thday of July, 1927.

VLADIMIR K. ZVVORYKIN'. ERROL B. SHAND. I

